I had a circline light fixture in my kitchen pantry. When the lights burned out twice in a year, after only being used a few minutes per day. I tried new bulbs and still nothing happened. I did some research and discovered the problem might be with the ballast. So I took off the old ballast to find the numbers on it, discovered this Sunpark was a suitable replacement, and ordered it.
Please note that you need a very basic electrical background to take off the old one and connect the new one: making sure the power is turned off, connect the black, white and ground wires on the ballast up to the ones from your house with wire nuts, and then attach the ballast back on to the fixture with screws. Carefully insert the plugs into your circline bulbs, making sure their wattage rating is within that of the ballast.